The present invention relates generally to reciprocating gas compressors. More particularly, the present invention relates to reciprocating compressors having piston-carried suction valves. With still more particularity, the present invention relates to an arrangement for guiding and retaining a suction valve on the piston of a reciprocating compressor.
Both efficiency and noise considerations are important in the design of reciprocating compressors. Efforts have been undertaken over the years to incorporate the suction valves of such compressors with or on a compressor""s pistons so as to take advantage of the reciprocating movement of the piston to assist in the opening and/or closing of the valve. By use of the reciprocating action of a piston to assist in the opening and/or closing of a suction valve, efficiency advantages are prospectively obtainable. However, and as noted in U.S. Pat. 5,775,886 to G. Terwilliger which is incorporated herein by reference, obtaining both low noise and high efficiency in a reciprocating compressor is complicated by the fact that an improvement in one often degrades the other.
It is the object of the invention of the Terwilliger ""886 patent to provide a novel gas compressor that improves the efficiency of a reciprocating compressor by the use of piston-carried suction valves and does so in a manner that addresses noise issues. In order to accomplish this goal, the ""886 patent identifies a design for a piston-carried suction valve one component of which is a sheath that is positioned around the top of the piston on which it is carried. The underside of the top of the sheath is juxtaposed the top of the piston and the sides of the sheath are disposed between the piston and the walls of the cylinder in which the piston reciprocates. The sheath moves both with and relative to the piston in carrying out its suction valve function.
In that regard, during the suction stroke of the piston, an opening formed in the top of the sheath of the Terwilliger compressor allows low pressure gas to flow through a suction chamber, defined by the piston-sheath combination, into a compression chamber. The compression chamber is defined between the top of the sheath and the bottom surface of a discharge valve which overlies the cylinder. Overall, the flow of suction gas in the compressor is through suction gas passages formed in the compressor""s cylinder block, through suction apertures defined in the sheath side wall that are in registry therewith, through the suction chamber defined by the piston-sheath combination, through the opening formed in the top of the sheath and into the compression chamber.
At the beginning of the compression stroke, the piston moves relative to and toward the sheath so as to force additional suction gas out of the suction chamber and into the compression chamber through the opening in the top of the sheath. The piston then continues its travel toward the discharge valve in concert with the sheath, a portion of the piston having moved into and closing the opening in the top of the sheath. The piston and sheath then act in cooperation and by their movement to compress the gas in the compression chamber.
Because the sheath and piston move both with and with respect to each other, provision must be made to guide and control the motion of the sheath with respect to the piston and to retain the sheath on the piston. In the case of the compressor of the Terwilliger ""886 patent, a plurality of integrally formed, resilient fingers extend from the sheath to engage and retain the sheath on the piston. The length of the fingers controls and limits the relative movement of the sheath with respect to the piston.
The sheath of the ""886 patent is, as noted therein, preferably fabricated from a thermoplastic material and the retaining fingers are therefore somewhat flexible. As such, the sheath and its fingers can be assembled to and over the top of a piston. If it becomes necessary, the resilient sheath fingers can be forced apart to allow for the separation and removal of the sheath from the piston.
Because the sheath fingers of the ""886 patent are relatively expensive and difficult to mold/fabricate and under some conditions can be susceptible to breakage, the need exists for a guide/retainer arrangement for a sheath which functions as a suction valve in a reciprocating compressor that is robust, is relatively easy to mold/fabricate and which facilitates the assembly of the sheath to the piston on which it is carried.
It is an object of the present invention to provide a reciprocating compressor in which the compressor""s suction valve apparatus is carried on and is actuated by the reciprocation of the compressor""s pistons.
It is a further object of the present invention to provide for the retention of a sheath on a piston in a reciprocating compressor where the sheath acts as a suction valve and moves both with and relative to the piston on which lit is carried.
It is a still further object of the present invention to provide for the robust, simplified and enhanced retention and guidance of a piston-carried sheath which functions as a suction valve in a reciprocating compressor by the use of retainers which are disposed and move within accommodating apertures in the sheath and which are secured to the wrist pin through which the piston is driven.
These and other objects of the present invention, which will better be appreciated by reference to the Description of the Preferred Embodiment which follows and the Drawing Figures attached hereto, are achieved in a reciprocating compressor having a sheathed piston where the sheath operates as a suction valve and moves both with and relative to the piston. The relative movement of the sheath with respect to the piston is guided and limited by retainers disposed at the ends of the piston""s wrist pin. The retainers have end faces which reside in accommodating apertures defined in the sidewall of the sheath member and both retain the sheath on the piston and limit the relative motion of the sheath with respect to the piston by the disposition of their end faces in the apertures defined in the sheath.
On the suction stroke, the piston and retainers move away from the discharge valve associated therewith and relative to the sheath until a first portion of the periphery of the end faces of the retainers make contact with an accommodating surface of the sheath apertures in which they are disposed. Once such contact is made, the sheath is pulled by and with the retainers so as to move in the same direction as the piston and a suction gas chamber is created between the top of the piston and the underside of the top of the sheath into which suction gas flows. Suction gas flows through suction gas apertures defined in the side of the sheath and into both the suction gas chamber defined between the piston and sheath and a compression chamber defined between the top of the sheath and the discharge valve associated with the cylinder in which the sheath/piston combination resides.
On the compression stroke, the piston and retainers move toward the discharge valve while the end faces of the retainers move within the sheath apertures in which they are disposed. The suction gas that has flowed into the suction volume defined between the piston and sheath during the suction stroke is forced thereoutof and into the compression chamber through an opening defined in the top of the sheath as a result of the initial relative motion of the piston and retainers with respect to the sheath. The movement of the piston toward the discharge valve progresses to a point where the piston comes into contact with the underside of the sheath and the opening defined in the top of the sheath comes to be closed by the contoured upper surface of the piston.
As a result of the contact of the piston with the sheath, the sheath is caused to move in direct concert with the piston toward the discharge valve. The cooperative movement of the piston and sheath toward the discharge valve and the closure of the opening in the top of the sheath causes the gas that exists in the compression chamber to be compressed. When the pressure in the compression chamber reaches a predetermined level, the discharge valve is forced open by such gas pressure and the compressed gas exits the cylinder therethrough.
Overall, by the disposition of appropriately configured retainers in accommodating apertures defined in the sidewall of the sheath, the sheath is retained on the piston and is caused to move relative thereto in a controlled manner by an arrangement that is relatively quiet, is robust, promotes compressor efficiency, is relatively simple and inexpensive, both with respect to its fabrication and assembly, and which eliminates certain of the disadvantages associated with prior sheath retention arrangements for reciprocating compressors in which suction valve apparatus is carried on the piston in the form of a sheath.